In processes for fabricating a semiconductor integrated circuit, sputtering is used for deposition of a Ti film for forming titanium silicide TiSi.sub.2 and for deposition of a titanium nitride film TiN used for a diffusion barrier layer.
Conventionally, for depositing a titanium nitride film using a sputtering method, a titanium target may be sputtered under an atmosphere containing a mixed gas of argon Ar and nitrogen N.sub.2, with the TiN film deposited on a substrate. As illustrated in FIG. 1, the TiN film is sputtered at a nitrogen ratio of over N1(%), and the deposition rate drops sharply. For depositing a titanium film using a sputtering method, the sputtering is carried out under an atmosphere of pure argon without any mixture of nitrogen (No in FIG. 1).
FIG. 1 is a graph illustrating the rate of deposition of a titanium nitride film depending on the ratio of nitrogen with conventional sputtering.
In case the TiN film is formed with a reactive sputtering method under an atmosphere of nitrogen having a ratio over N1, the surface of the titanium target is corroded to form a titanium nitride film on the surface of the titanium target. Therefore, when the titanium nitride film formed on the surface of the titanium target is sputtered under an atmosphere of mixed gas of N.sub.2 and Ar, a titanium nitride film is formed on the surface of the substrate.
The titanium nitride film formed through the foregoing processes serves as a diffusion barrier layer at an interface of, such as, Al/Si or Cu/Si, in a fabrication process of a semiconductor element. The titanium nitride films deposited through the foregoing processes, however, have a columnar structure with a grain size of about 200 .ANG.. Therefore, it has a porous structure with voids between the grains.
Such a columnar structured titanium nitride film, allowing diffusion to progress through the grain boundaries, may allow pin holes to form, making the nitride film unable to serve as a diffusion barrier layer. Moreover, though a single crystal titanium nitride film has a resistivity of 23 .mu..OMEGA..multidot.cm, the titanium nitride film deposited through the above reactive sputtering method has an increased resistivity of 200 to 1000 .mu..OMEGA..multidot.cm due to the columnar structure.
Therefore, in order to have a titanium nitride film functioning perfectly as a diffusion barrier with reduced resistivity, a titanium nitride film of, not a porous structure, but, a fine-textured structure, should be obtained.